The present invention relates to a hydraulic clamping device for the axial clamping of bodies of rotation, for example, disk-shaped or roller-shaped workpieces or tools, especially hobs, onto a revolving mandrel, having a base body fixed to the mandrel and a rotary piston which is suspended in a floating manner inside the base body and is axially slidable relative to the base body via a closed-circuit hydraulic system and pressure elements such as setscrews and which tightly clamps the workpiece or tool in an axial direction.
Hydraulic clamping devices of the aforementioned kind represent an improvement of mechanical clamping devices since they are able to provide clamping forces increased by several magnitudes. Such great axial clamping forces are necessary, for example, in order to maintain the position and the concentricity of a revolving tool during the machining process of a workpieces under high cutting loads.
Generally, the hydraulic clamping device is screwed onto the free end of a mandrel that is carrying the tool, for example, a cutter, until it abuts at the cutter. By screwing in at least one radially or axially arranged setscrew, a rotary, piston which is suspended in a floating manner inside the base body is pushed outward in an axial direction. Despite the lesser mechanical force required in comparison with a mechanical clamping device, the hydraulic force transmission achieves a substantially higher axial clamping force.
Since the rotary piston is suspended in a floating manner, an uneven sliding of the rotary piston in the outward direction may result from an uneven internal pressure distribution and/or uneven friction conditions. This may cause a radial displacement of the tool or an axial deviation, a so-called bending, of the free end of the mandrel. In some cases, the rotary piston floating on the hydraulic fluid "cushion" may not withstand the high cutting force loads so that concentricity deviations of the tool may occur also. When the use of auxiliary means such as a hammer is not desired, a manual adjustment of the tools, with known clamping devices, into a so-called center cradle, i.e., between two tips, is only possible by clamping the tool repeatedly until the ideal position is essentially reached. However, this method of trial and error is not very satisfactory, since the reduction of time between productive operation intervals of the machines is an important factor in manufacturing.
It is therefore an object of the present invention to improve the axial rigidity of the clamping device, to provide a directed, easy and fast adjustment of concentricity errors during the clamping of the tool and also to alleviate radial play during operation.